Unless otherwise indicated herein, the materials described in this section are not prior art to the claims and are not admitted to be prior art by inclusion in this section.
To provide cellular wireless communication service, a wireless service provider typically operates a radio access network (RAN) that includes a number of base stations that radiate to define wireless coverage areas, such as cells and cell sectors, in which wireless communication devices (WCDs) such as cell phones, tablet computers, tracking devices, embedded wireless modules, and other wirelessly-equipped communication devices, can operate. In turn, each base station may be coupled with network infrastructure that provides connectivity with one or more transport networks, such as the public switched telephone network (PSTN) and/or the Internet for instance. With this arrangement, a WCD within coverage of the RAN may engage in air interface communication with a base station and may thereby communicate via the base station with various remote network entities or with other WCDs served by the base station.
In general, a RAN may operate in accordance with a particular air interface protocol or “radio access technology,” with communications from the base stations to WCDs defining a downlink or forward link and communications from the WCDs to the base stations defining an uplink or reverse link. Examples of existing air interface protocols include, without limitation, Orthogonal Frequency Division Multiple Access (OFDMA (e.g., Long Term Evolution (LTE) or Wireless Interoperability for Microwave Access (WiMAX)), Code Division Multiple Access (CDMA) (e.g., 1×RTT and 1×EV-DO), and Global System for Mobile Communications (GSM), among others. Each protocol may define its own procedures for registration of WCDs, initiation of communications, handoff between coverage areas, and functions related to air interface communication.
In accordance with the air interface protocol, each coverage area may operate on one or more carrier frequencies or blocks of frequencies (e.g., frequency bands, such as 698-960 MHz, 1610-2025 MHz, etc.) and may define a number of air interface channels for carrying information between the base station and WCDs. These channels may be defined in various ways, such as through frequency division multiplexing, time division multiplexing, and/or code-division multiplexing, for instance. By way of example, each coverage area may define a pilot channel, reference channel, or other resource on which the base station may broadcast a pilot signal, reference signal, or the like that WCDs may detect as an indication of coverage and may measure to evaluate coverage strength. As another example, each coverage area may define one or more uplink control channels or other resources on which WCDs may transmit control messages to the base station. And each coverage area may define one or more downlink control channels or other resources on which the base station may transmit control messages or other information to WCDs. Further, each coverage area may define one or more traffic channels or other resources for carrying bearer communication traffic such (e.g., user traffic or application level traffic) as voice data and other data between the base station and WCDs.
When a WCD first powers on or enters into a base station's coverage area, the WCD may register with the RAN in that coverage area by transmitting a registration request, such as an attach request, to the base station serving that coverage area. The attach request may cause the base station or associated infrastructure to authenticate and authorize the WCD for service by the base station and to reserve network resources for use to serve the WCD. In particular, the attach request may result in setup of one or more virtual bearer connections extending in the network between the base station and one or more transport networks and extending over the air interface as a radio link between the base station and the WCD. Each such bearer may have a particular service level and intended use. For instance, one such bearer may be a default data bearer for use to carry general data communications to and from the WCD. Whereas, another such bearer may be a signaling bearer for use to carry packet-based session setup signaling such as Session Initiation Protocol (SIP) signaling between the WCD and a network communication server, and another such bearer may be a dedicated bearer that provides a guaranteed minimum bit-rate for carrying real-time media communications for instance. Certain bearers may be established for the WCD at the time of the WCD initially attaching with the base station, while others, such as a guaranteed minimum bit-rate bearer, may be established for the WCD (i.e., “assigned” to the WCD) after the WCD has initially attached with the base station (e.g., when a WCD initiates a voice over LTE (VoLTE) call or other such real-time communication session, for instance).
Once the WCD is attached with a base station, the WCD may operate in a connected mode or an idle mode. In the connected mode, the WCD may engage in communication of bearer data (e.g., application layer communications, such as SIP signaling, voice communication, video communication, file transfer, gaming communication, or the like), transmitting bearer data on uplink traffic channel resources to the base station and receiving bearer on downlink traffic channel resources from the base station.
After a timeout period of no bearer data communication between the base station and the WCD (possibly with respect to a particular bearer), or for other reasons, the WCD may transition from the connected mode to the idle mode, with the base station releasing the radio link portion of one or more bearer connections assigned to the WCD, so as to conserve air interface resources while still having the one or more bearer connections assigned to the WCD. In the idle mode, the WCD may then simply monitor a downlink control channel to receive overhead information and to check for any page messages for the WCD. Further, while the WCD is operating in the idle mode, the WCD may continue to regularly scan pilot or reference signals on both the carrier frequency on which the WCD is idling and other carrier frequencies as well, to help ensure that the WCD continues to operate on carrier frequencies providing the strongest coverage.